This application relates to products for the treatment of viral infections, in particular HIV infections, using the known antiviral compounds efavirenz (tradename Sustiva, also known as EFV), emtricitabine (tradename Emtriva, also known as FTC) and tenofovir DF (disoproxil fumarate, also known as TDF) (tradename Viread, sold in combination with emtricitabine under the tradename Truvada).
The Truvada product is produced by wet granulation of emtricitabine and tenofovir DF (WO 04/64845), which under the circumstances produces a chemically stable dosage form. This product does not contain efavirenz.
HIV therapy using efavirenz as well as emtricitabine and tenofovir DF has been considered desirable (hereafter “triple combination”; see WO 04/64845). Manufacturing a commercially viable triple combination product, however, would require that the final product meet stringent FDA requirements for bioequivalence to the commercial products, Viread (tenofovir disoproxil fumarate), Emtriva (emtricitabine), and Sustiva (efavirenz), and that the tablet be of suitable size for patients to easily swallow.
Initial efforts to simply combine the three drugs (active pharmaceutical intermediates, or APIs) into a unitary, essentially homogeneous composition manufactured by wet granulation failed to produce a chemically stable tablet. The tenofovir DF in this combination tablet was highly unstable and rapidly degraded in stability studies. The efavirenz formulation was unexpectedly incompatible with tenofovir DF, a result now attributed to the surfactant (sodium lauryl sulfate) found in the efavirenz portion of the formulation.
Another attempt was made to produce the triple combination, this time using a dry granulation of the three part combination and omitting the surfactant. This resulted in a tablet that failed to achieve bioequivalence with respect to efavirenz in human clinical trials. The peak efavirenz concentration in the blood stream and total drug exposure (Cmax and AUC) were both below the parameters determined for the commercial comparator, Sustiva (efavirenz) tablets. The inventors concluded that at least the surfactant in the triple combination (efavirenz/emtricitabine/tenofovir disoproxil fumarate) tablets was necessary to achieve bioequivalence to Sustiva.
Next, combination tablets were manufactured by wet granulating the efavirenz component with the surfactant and other excipients, separately manufacturing the Truvada component using dry granulation, mixing the granulates together, compressing the mixture into tablets, and then film-coating the tablets. Unexpectedly, this approach also failed to produce the desired bioequivalence in between the commercial product, Sustiva (efavirenz), and clinical trial material (i.e., proposed commercial triple combination product). A novel and inventive step was needed to overcome the shortcomings of more straight-forward approaches to a triple combination dosage form.
Copending U.S. Ser. No. 60/771,353 (filed of even date and expressly incorporated herein by reference) is directed to solving another obstacle encountered in the preparation of the triple combination dosage form, that of reducing the size of the combined product. While the prior art reports the successful manufacture of chemically stable Truvada preparations (WO04/64845), these preparations contain relatively low proportions of excipient to API. Increasing the proportion of excipients and wet granulating the three API combination unexpectedly resulted in a preparation in which the tenofovir DF was highly unstable. As reported in U.S. Ser. No. 60/771,353, it was believed that use of sufficient water to accomplish the wet granulation of efavirenz (which has relatively low solubility in comparison to emtricitabine and tenofovir DF) caused the latter two APIs to dissolve into a eutectic mixture. The eutectic mixture dried during granulation to form a glassy or amorphous product in which the tenofovir DF is chemically unstable in comparison to the crystalline API. Supplying enough excipient to ameliorate the effect of the excess water was not consistent with the objective of obtaining a triple combination oral dosage form of manageable proportions.
As described further in U.S. Ser. No. 60/771,353, this obstacle was overcome by dry granulating the emtricitabine and tenofovir DF composition, i.e., granulating the composition without contacting same with a destabilizing amount of liquid water. Omitting water (particularly, liquid water) or reducing the presence of water to an insubstantial amount eliminates the disadvantageous formation of a eutectic mixture and enhances the stability of the resulting pharmaceutical product.
Despite the advantages conferred by dry granulation of the emtricitabine/tenofovir DF component, it was still necessary to overcome the unexpected incompatibility of tenofovir DF and the surfactant used in the Sustiva formulation.